Actively-cooled distribution plate for reducing reactive gas temperature in a plasma processing system

ABSTRACT

A plasma processing system ( 10 ) is provided, having processor chamber walls ( 53 ) and/or a gas distribution or baffle plate ( 54 ) equipped with integral cooling passages ( 80, 156 ) for reducing an operating temperature thereof during processing of a wafer ( 18 ) by the system. Cooling medium inlets ( 158, 82 ) and outlets ( 160, 86 ) are connected to the cooling passages to permit circulation of a cooling medium through the cooling passages. Preferably, the chamber walls ( 53 ) and the gas distribution or baffle plate ( 54 ) are comprised of low-alloy anodized aluminum and the cooling passages are machined directly therein. The cooling medium may be either liquid (e.g., water) or gas (e.g., helium or nitrogen). The baffle plate ( 54 ) comprises a generally planar, apertured, gas distribution central portion ( 74 ) surrounded by a flange ( 78 ), into both of which the cooling passages may extend. The cooling passages in the chamber walls ( 53 ) and those in the gas distribution or baffle plate ( 54 ) may be in communication with one another so as to permit them to share a single coolant circulating system. Alternatively, the cooling passages in the chamber walls ( 53 ) and those in the gas distribution or baffle plate ( 54 ) may not be in communication with one another, so as to provide independent circulating systems (gas or liquid) for each, thereby enabling independent temperature control and individual flow control thereof. In operation, the cooling medium in the chamber wall cooling passages ( 156 ) is maintained approximately within the range of 15° C.-30° C., and the cooling medium in the gas distribution or baffle plate cooling passages ( 80 ) is maintained approximately within the range of 15° C.-80° C. Periodically, the lower baffle plate may alternatively be operated at up to 250° C. to remove process residues from the surface of the plate that may otherwise condense and remain on the surface at lower operating temperatures (e.g., 15° C.-80° C.).

RELATED APPLICATION

[0001] The following U.S. patent application is incorporated byreference herein as if it had been fully set forth: application Ser.No.: ______, filed on ______, entitled Gas Distribution Plate Assemblyfor Providing Laminar Flow Across the Surface of a Substrate.

FIELD OF THE INVENTION

[0002] The present invention relates generally to the field ofsemiconductor plasma processing systems such as photoresist ashers, andmore specifically to a actively-cooled distribution plate for reducingreactive gas temperature for use in such systems.

BACKGROUND OF THE INVENTION

[0003] In the manufacture of integrated circuits, photolithographytechniques are used to form integrated circuit patterns on a substrate,such a silicon wafer. Typically, the substrate is coated with aphotoresist, portions of which are exposed to ultraviolet (UV) radiationthrough a mask to image a desired circuit pattern on the photoresist.The portions of the photoresist left unexposed to the UV radiation areremoved by a processing solution, leaving only the exposed portions onthe substrate. These remaining exposed portions are baked during aphotostabilization process to enable the photoresist to withstandsubsequent processing.

[0004] After such processing, in which the integrated circuit componentsare formed, it is generally necessary to remove the baked photoresistfrom the wafer. In addition, residue that has been introduced on thesubstrate surface through processes such as etching must be removed.Typically, the photoresist is “ashed” or “burned” and the ashed orburned photoresist, along with the residue, is “stripped” or “cleaned”from the surface of the substrate.

[0005] One manner of removing photoresist and residues is by rapidlyheating the photoresist-covered substrate in a vacuum chamber to apreset temperature by infrared radiation, and directing amicrowave-energized reactive plasma toward the heated substrate surface.In the resulting photoresist ashing process, wherein the reactive plasmareacts with the photoresist, the hot reactive gases in the plasma addheat to the surface of the substrate by means of convection. Heat energyon the order of 100 millliwatts per square centimeter (mW/cm²) is alsoadded to the wafer as a result of the surface reaction. Excessive heaton the surface of the wafer can damage devices or portions thereof whichhave been formed on or in the wafer. In addition, excessive heat on thesurface of the wafer can cause photoresist cracking during, for example,high-density ion implanted (HDII) wafer ash processes.

[0006] Reducing the temperature of the ashing process in the chamberwill slow the reaction rate and thus the amount of heat added to thewafer by the surface reaction. However, the gas temperature, which is afunction of the gas mixture and the applied microwave power, will remainunaffected by the reduced process temperature. The problem isexacerbated if the process includes a reaction catalyst such as carbontetrafluoride (CF₄) which tends to increase the rate of reaction due toincreased production of atomic oxygen. As a result, thecatalyst-assisted process results in higher temperature gases, even atlower process temperatures.

[0007] A typical plasma processing apparatus is shown in U.S. Pat. No.5,449,410 to Chang et al. wherein an aluminum baffle plate or showerheadis provided for distributing gas into a plasma chamber. However, nomeans of controlling the temperature of the gas is shown. Accordingly,the apparatus shown will suffer from the adverse effects of hightemperature gases as described above.

[0008] In addition, because individual wafers are processed in a serialfashion by known single-wafer process chambers, systems such as thatshown in U.S. Pat. No. 5,449,410 exhibit a phenomenon known as the“first wafer effect”, which refers to secondary heating of subsequentwafers caused indirectly by the heating of the first-processed wafer.Specifically, upon completion of processing of the first wafer, theheated processed wafer and the process chamber side walls radiate heattoward the gas distribution baffle plate (typically made from quartz).The heated quartz plate then indirectly provides a secondary heatingmechanism for subsequent wafers that are processed in the chamber. As aresult, the first and subsequent wafers processed by the system exhibitprocess non-uniformities.

[0009] Still another problem with known baffle plates is that thermalgradients develop across the surface of the baffle plate. Because suchbaffle plates are typically made of quartz, due to their ability towithstand high process temperatures, they tend to exhibit poor thermalconductivity as well as undesirable infrared (IR) wavelength absorptioncharacteristics. In addition, the temperature of a quartz baffle platecan be difficult to control if IR wavelength energy is absorbed from thewafer with no means for sinking or dissipating the absorbed radiantenergy. As a result, process uniformity and system throughput areadversely affected.

[0010] Thus, it is an object of the present invention to provide amechanism for reducing the temperature of gases used in a waferprocessing system such as a photoresist asher to prevent damage to thewafer during the ashing process. It is a further object of the presentinvention to reduce the temperature of reactive gases required by lowtemperature processes, by incorporating cooling means into a gasdistribution or baffle plate used therein. It is yet a further object ofthe invention to improve wafer-to-wafer process uniformity in suchprocesses, by eliminating secondary heating caused by the “first wafereffect”. It is still a further object of the invention to provide amechanism for providing a relatively flat temperature profile across thesurface of the gas distribution or baffle plate, thereby improving bothhigh and low temperature within-wafer process uniformity.

SUMMARY OF THE INVENTION

[0011] A plasma processing system is provided, having processor chamberwalls and/or a gas distribution or baffle plate equipped with integralcooling passages for reducing an operating temperature thereof duringprocessing of a wafer by the system. Cooling medium inlets and outletsare connected to the cooling passages to permit circulation of a coolingmedium through the cooling passages. Preferably, the chamber walls andthe gas distribution or baffle plate are comprised of aluminum and thecooling passages are machined directly therein. The cooling medium maybe either liquid (e.g., water) or gas (e.g., helium or nitrogen).

[0012] The baffle plate comprises a generally planar, apertured, gasdistribution central portion surrounded by a flange, into both of whichthe cooling passages may extend. The cooling passages in the chamberwalls and those in the gas distribution or baffle plate may be incommunication with one another so as to permit them to share a singlecoolant circulating system. Alternatively, the cooling passages in thechamber walls and those in the gas distribution or baffle plate may notbe in communication with one another, so as to provide independentcirculating systems (gas or liquid) for each, thereby enablingindependent temperature control and individual flow control thereof. Inoperation, the cooling medium in the chamber wall cooling passages ismaintained approximately within the range of 15° C.-30° C., and thecooling medium in the gas distribution or baffle plate cooling passagesis maintained approximately within the range of 15° C.-80° C.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a sectional view of a photoresist asher into which isincorporated a first embodiment of a baffle plate constructed accordingto the present invention;

[0014]FIG. 2 is a partial cutaway, perspective view of the firstembodiment of the baffle plate of FIG. 1;

[0015]FIG. 3 is a partial cutaway, perspective view of a photoresistasher chamber assembly into which is incorporated a second embodiment ofa baffle plate assembly constructed according to the present invention;

[0016]FIG. 4 is a partial cutaway, perspective view of a lower baffleplate of the second embodiment of the baffle plate assembly of FIG. 3;

[0017]FIG. 5 is a plan view of the baffle plate assembly shown in FIG.3;

[0018]FIG. 6 is a sectional view of the baffle plate assembly of FIG. 5,taken along the lines 6-6; and

[0019]FIG. 7 is a sectional view of the baffle plate assembly of FIG. 6,taken along the lines 7-7.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

[0020] Referring now to the drawings, FIG. 1 discloses a prior artphotoresist asher 10, comprising a gas box 12; a microwave plasmagenerator assembly 14; a process chamber 16 defining an interior cavity17 in which is heated a semiconductor substrate such as a wafer 18; anda radiant heater assembly 20 for heating the wafer 18, situated at thebottom of the process chamber. A temperature probe 24, such as athermocouple, is used to monitor the temperature of the wafer 18. Avacuum pump 26 is used to evacuate the process chamber 16 for processesrequiring vacuum conditions.

[0021] A monochromator 28 is used to monitor the optical emissioncharacteristics of gases within the chamber to aid in process endpointdetermination. The wafer 18 is introduced into and removed from theprocess chamber via an appropriate load lock mechanism (not shown) viaentry/exit passageway 30. Although the present invention is shown asbeing implemented within a photoresist asher, it may also be used inother semiconductor manufacturing equipment, such as residue removal andstrip processes.

[0022] In operation, a desired mixture of gases is introduced into aplasma tube 32 from gas box 12 through an inlet conduit 34. The plasmatube 32 is made of alumina (Al₂O₃) or sapphire to accommodate fluorinechemistries without etching or other degradation. The gases forming thedesired mixture are stored in separate supplies (not shown) and mixed inthe gas box 12 by means of valves 36 and piping 38. One example of adesired gas mixture is forming gas (primarily nitrogen with a smallpercentage of hydrogen), and oxygen. A fluorine containing gas such ascarbon tetrafluoride (CF₄) may be added to the gas mixture to increaseashing rates for certain processes.

[0023] The desired gas mixture is energized by the microwave plasmagenerator assembly 14 to form a reactive plasma that will ashphotoresist on the wafer 18 in the process chamber 16 when heated by theradiant heater assembly 20. A magnetron 40 generates microwave energythat is coupled to a waveguide 42. Microwave energy is fed from thewaveguide through apertures (not shown) in microwave enclosure 44, whichsurrounds the plasma tube 32.

[0024] An outer quartz cooling tube 46 surrounds the plasma tube 32,slightly separated therefrom. Pressurized air is fed into the gapbetween the tubes 32 and 46 to effectively cool the tube 32 duringoperation. The microwave enclosure 44 is segmented into sections shownby phantom lines 45. Segmentation of the enclosure 44 allows uniformmicrowave power distribution across the length of the alumina orsapphire plasma tube, and protects it from overheating by preventing anunacceptably large thermal gradient from developing along its axiallength when suitable input power is provided. Each segment of theenclosure 44 is separately fed with microwave energy that passes throughthe quartz tube 46 and the alumina or sapphire tube 32 passingtherethrough.

[0025] The gas mixture within the plasma tube 32 is energized to createa plasma. Microwave traps 48 and 50 are provided at the ends of themicrowave enclosure 44 to prevent microwave leakage. Energized plasma(typically having a temperature of about 150° C.) enters the processchamber 16 through an opening 1 in the top wall 52 thereof.

[0026] Positioned between the top wall 52 of the plasma chamber 16 andthe wafer 18 being processed is a first preferred embodiment of theinventive gas distribution (or baffle) plate 54 of the presentinvention. Although shown as single member baffle plate, it iscontemplated that the baffle plate may take the form of a dual-layeredbaffle plate assembly 154 (FIGS. 3-7) comprising upper and lower baffleplates. In either embodiment, the baffle plate 54 (FIGS. 1-2) and thebaffle plate assembly 154 (FIGS. 3-7) evenly distribute the reactiveplasma across the surface of the wafer 18 being processed, and providemeans for cooling the gases within the plasma to achieve desired processresults.

[0027] With reference back to FIG. 1, in operation, the reactive plasmapasses through the baffle plate 54 and ashes the photoresist on thewafer 18. The radiant heater assembly 20 comprises a plurality oftungsten halogen lamps 58 residing in a reflector 56 that reflects andredirects the heat generated by the lamps toward the backside of thewafer 18 positioned within the process chamber 16 on quartz or ceramicpins 68. One or more temperature sensors 72, such as thermocouples, aremounted on the interior of process chamber side wall 53 to provide anindication of wall temperature.

[0028] The baffle plate 54 shown in the photoresist asher 10 of FIG. 1is shown in greater detail in FIG. 2, which is designed forincorporation into a 200 millimieter (mm) wafer processing system. Thebaffle plate 54 comprises a generally planar gas distribution centralportion 74, having apertures 76 therein, surrounded by a flange 78. Theflange 78 surrounds the central portion and seats intermediate theprocess chamber side wall 53 and top wall 52 (see FIG. 1). Seals 79 and81, respectively, provide air tight connections between the flange 78and the side wall 53, and between the flange 78 and the top wall 52. Theseals 79 and 81 reside in grooves 83 and 85, respectively, located inthe flange 78 (see FIG. 2). The flange 78 also provides mounting holes84 for mounting to the top wall 52 and side wall 53.

[0029] The central apertured portion 74 of the baffle plate 54 isprovided with internal cooling passages 80 connected to cooling mediuminlet 82 and outlet 86. The cooling passages 80 reduce the operatingtemperature of the baffle plate 54, and extend about its central portion74 in a configuration that avoids intersection with any of the apertures76. In the preferrred embodiment, water is used as the cooling medium,although other liquids (e.g., oil) or gases (e.g., helium or nitrogen)having a high heat capacity are contemplated. As reactive gases passthrough the apertures 76, the cooled baffle plate functions as a heatexchanger to remove heat from the reactive gases, thereby reducing itstemperature. The baffle plate 54 also minimizes mobile ion contaminationthat can potentially cause wafer device damage, for example, weakeningthe dielectric strength of gate oxides. I

[0030] The baffle plate is preferably formed from a single piece oflow-alloy anodized aluminum (e.g., Alcoa type C-276), whichsignificantly improves the heat transfer characteristics of the baffleplate over known quartz baffle plates. The use of aluminum also permitsthe cooling passages to be drilled or machined directly therein. Thismakes the baffle plate less sensitive to inconsistencies in thereflector heating system and parasitic heating from the wafer, andallows for operation at a substantially uniform temperature.

[0031] The use of aluminum also blocks a large percentage of ultraviolet(UV) energy emanating from the plasma tube that would otherwise maketemperature control more difficult and possibly cause wafer devicedamage. Operating at a uniform surface temperature and minimizingexposure to UV radiation provides a substantial improvement in reactionrate uniformity across the surface of the wafer over known quartz baffleplates. In addition, maintaining a consistent baffle plate temperatureeliminates the “first wafer effects” due to parasitic heating of thebaffle plate as successive wafers are placed in the process chamber andheated to process temperature by the radiant heating system.

[0032]FIG. 3 shows a second embodiment of the invention, in which thebaffle plate takes the form of the baffle plate assembly 154, which isdesigned for incorporation into a 300 millimeter (mm) wafer processingsystem. FIG. 3 is a partial cutaway, perspective view of a 300 mmphotoresist asher chamber assembly 100 (shown without an associatedradiant heater assembly) into which is incorporated this baffle plateassembly 154. The baffle plate assembly 154 comprises a generally planarupper baffle plate 155 and lower baffle plate 157 positioned generallyparallel to each other and separated from one another. The assembly 154is shown attached to the 300 mm process chamber 116. The upper and lowerbaffle plates 155 and 157, respectively, are provided with apertures 175and 176. The apertures 175 in the upper baffle plate are slightly largerthan the apertures 176 in the lower baffle plate. A process chamberaccess port 128 is provided for either a vacuum pump or a monochromator.

[0033] In this second embodiment of the invention, both the baffle plateassembly 154 and the process chamber 116 may be provided with activecooling mechanisms. With regard to the process chamber, internal coolingchannels 156 are provided in the side walls 153 thereof. Cooling mediuminlets 158 and 160, respectively, are provided to permit entry and exitof a cooling medium, such as water, and out of the cooling channels. Theprocess chamber side walls 153 are preferably formed from low-alloyanodized aluminum (e.g., Alcoa type C-276), which permits the coolingpassages 156 to be drilled or machined directly therein, thereby makingthe side walls less sensitive to inconsistencies in the reflectorheating system, and allowing for operation at a substantially uniformprocess temperature.

[0034] Although the lower baffle plate 157 provided with active cooling,as explained further below, the upper baffle 155 plate is also notprovided with an active cooling mechanism. The upper baffle plate 155 iscomprised merely of a solid, apertured quartz plate, attached to thelower plate by means of posts 161 at attachment points 159 (see FIGS. 4and 6). The upper baffle plate, which may be sapphire coated, functionsto divert a portion of the hot gaseous plasma which does not passthrough its apertures 175 radially outward, so as to prevent theradially inward potion of the wafer 18 being processed from overheatingand to promote reaction rate uniformity. A non-apertured sapphire plate177 (FIGS. 5 and 6) covers the central portion of the upper baffle plate155.

[0035] The active cooling mechanism provided by the lower baffle plate157 is more clearly shown in its partial cutaway, perspective view inFIG. 4. The lower baffle plate 157 comprises a generally planar gasdistribution central portion 174, having the apertures 176 therein,surrounded by a flange 178. The flange 178 provides the surface to whicha top wall 181 of the process chamber 116 may be attached using mountingholes 184. Seal 179 provides an airtight connection between the flange178 and the side wall 153 (FIG. 3). The seal 79 resides in a groove 183in flange 178 (FIG. 4).

[0036] The central apertured portion 174 of the baffle plate 157 isprovided with internal cooling passages 180 connected to cooling mediuminlet 182 and outlet 186 (FIG. 3). As shown in FIGS. 4 and 6, thecooling passages 180 may extend from the flange 178 into and about thecentral portion 174 in a configuration that avoids intersection with anyof the apertures 176. One preferred configuration is shown in FIG. 7.

[0037] Still further, the cooling channels may also extend into theprocess chamber top wall. These individual cooling subsystems of thesestructural components (i.e., baffle plate, side walls and top wall)function to reduce the operating temperatures thereof. The coolingsubsystems may either share a single gas or liquid coolant circulatingsystem, or may be provided with independent circulating systems (gas orliquid) so as to provide independent temperature control and individualflow control thereof. Also, in embodiments of the invention whereinactive cooling of the process chamber side walls and top wall are alsoprovided, by maintaining these chamber surfaces at between 15° C.-30° C.(just above the dew point), the wafer can remain sufficiently cool toprevent photoresist cracking during, for example, high-density ionimplanted (HDII) wafer ash processes.

[0038] The cooling passages minimize the spatial temperature gradientacross the surface of the lower baffle plate 157 and maintain the entiresurface of the baffle plate at a uniform temperature. The cooling mediumsuch as water (maintained, e.g., at 15° C.-80° C.) flows into thechannels 180 via inlets 182 and flows out via outlets 186 (FIGS. 5 and7), using a deionized water recirculating system including an air-cooledchiller assembly. The chiller assembly has a heat removal capacitygreater than the heat generation rate of the process chamber even duringrapid heating of the wafer.

[0039] Although water is used in the preferred embodiment as the coolingmedium, other high heat capacity liquids or gases may be used, dependingupon the required operating temperature of the lower baffle plate. Forexample, the lower baffle plate can be operated at up to 250° C. toremove process residues from the surface of the plate. These residuesmay otherwise condense and remain on the surface of the lower plate ifnot periodically exposed to higher temperatures during wafer processing.At lower operating temperatures (e.g., 15° C.-80° C.), as reactive gasespass through the apertures 176, the lower baffle plate 157 functions asa heat exchanger to remove heat from the reactive gases, therebyreducing their temperature.

[0040] The lower baffle plate 157 is preferably formed from a singlepiece of low-alloy anodized aluminum (e.g., Alcoa type C-276), whichimproves the heat transfer characteristics of the baffle plate overknown quartz baffle plates. The use of aluminum also permits the coolingpassages to be drilled or machined directly therein. This makes thebaffle plate less sensitive to inconsistencies in the reflector heatingsystem and parasitic heating from the wafer, and allows for operation ata substantially uniform temperature.

[0041] The use of aluminum also blocks a large percentage of ultraviolet(UV) energy emanating from the plasma tube that would otherwise maketemperature control more difficult and possibly cause wafer devicedamage. Operating at a uniform surface temperature and minimizingexposure to UV radiation provides a substantial improvement in reactionrate uniformity across the surface of the wafer over known quartz baffleplates. In addition, maintaining a consistent baffle plate temperatureeliminates the “first wafer effects” due to parasitic heating of thebaffle plate as successive wafers are placed in the process chamber andheated to process temperature by the radiant heating system.

[0042] A pressure drop across the lower baffle plate 157 distributes thegas flow across the upper surface of the plate, in addition toincreasing the heat transfer rate between the gas and the platesurfaces. This same effect, in combination with the upper quartz plate155, reduces mobile ion contamination that can potentially cause devicedamage such as compromising the dielectric strength of gate oxides. Thecombination of the quartz upper plate 155 and the aluminum lower plate157 in the dual-layered baffle plate assembly 154 has been found to besuitable for use in the corrosive conditions found in a process chamberused for photoresist removal, even when corrosive element-producinggases such as CF₄ are utilized.

[0043] In operation, the systems 10 (200 mm) and 100 (300 mm) have beenoperated using the water-cooled baffle plate 157 and the baffle plateassembly 154, respectively, at maximum microwave power, under whichconditions the gas temperatures have been reduced below the minimumexpected process temperature, typically 80° C. Also, it has beenpossible to obtain a relatively flat temperature profile across thesurface of the wafer during processing, resulting in reduced processnon-uniformity due to the gas and radiation cooling effects of thecooled lower baffle plate. Active cooling of the lower baffle plate alsoreduces thermal loading of the baffle plate by the first-processed waferto improve wafer-to-wafer process uniformity.

[0044] In one example, a 270° C. ashing process was run while flowingwater at 30° C. through the lower baffle plate 157 at a flow rate of 0.4gallon per minute (gpm). An ash rate of 5.59 microns per minute wasachieved with a 2.25% ash rate non-uniformity across the across thewafer. An ash rate of 5.66 microns per minute with a 6.2% ash ratenon-uniformity across the wafer was obtained with a prior quartznon-actively cooled baffle blate. These test results show that using anactively-cooled baflle plate provides significant improvements in thearea of process uniformity with minimal effect on ash rates.

[0045] Accordingly, a preferred embodiment of a method and system forcooling the reactive gases in a plasma processing system, as well as thewafer being processed, has been described. With the foregoingdescription in mind, however, it is understood that this description ismade only by way of example, that the invention is not limited to theparticular embodiments described herein, and that variousrearrangements, modifications, and substitutions may be implemented withrespect to the foregoing description without departing from the scope ofthe invention as defined by the following claims and their equivalents.

What is claimed is:
 1. A plasma processing system (10) comprising: (i) aplasma generator (14); (ii) a processing chamber (16) having an interiorprocessing cavity (17) in communication with said plasma generator (14)such that plasma within said generator may pass into said cavity andreact with the surface of a substrate (18) residing therein; saidprocessing chamber comprising walls (53) which at least partially definesaid cavity (17), said walls provided with first cooling passages (156)for reducing an operating temperature thereof; (iii) a cooling mediuminlet (158) and a cooling medium outlet (160) connected to said firstcooling passages (156) to permit circulation of a cooling medium throughsaid first cooling passages; and (iv) a radiant heater assembly (20) forheating the substrate (18).
 2. The plasma processing system (10) ofclaim 1, wherein said first cooling passages (156) are internal to saidwalls (53).
 3. The plasma processing system (10) of claim 2, whereinsaid walls (53) are comprised of low-alloy anodized aluminum and saidfirst cooling passages (156) are machined into said walls.
 4. The plasmaprocessing system (10) of claim 2, wherein said cooling medium is aliquid.
 5. The plasma processing system (10) of claim 4, wherein saidcooling medium is water.
 6. The plasma processing system (10) of claim2, wherein said cooling medium is a gas.
 7. The plasma processing system(10) claim 6, wherein said cooling medium is helium or nitrogen.
 8. Theplasma processing system (10) of claim 2, further comprising a baffleplate (54) positioned between said plasma generator (14) and saidprocessing cavity (17), said baffle plate (54) having (i) apertures (76)therein for permitting the plasma to pass therethrough; (ii) secondcooling passages (80) for accepting a flow of cooling medium to reducean operating temperature of said baffle plate; and (iii) a coolingmedium inlet (82) and a cooling medium outlet (86) connected to saidsecond cooling passages (80) to permit circulation of a cooling mediumtherethrough.
 9. The plasma processing system (10) of claim 8, whereinsaid baffle plate (54) comprises a generally planar, apertured, gasdistribution central portion (74) surrounded by a flange (78), saidsecond cooling passages extending from said flange into said aperturedcentral portion.
 10. The plasma processing system (10) of claim 8,wherein said first cooling passages (156) and said second coolingpassages (80) are in communication with one another so as to permit themto share a single coolant circulating system.
 11. The plasma processingsystem (10) of claim 8, wherein said first cooling passages (156) andsaid second cooling passages (80) are not in communication with oneanother.
 12. The plasma processing system (10) of claim 11, wherein thecooling medium in said first cooling passages (156) is maintainedapproximately within the range of 15° C.-30° C., and the cooling mediumin said second cooling passages (80) is maintained approximately withinthe range of 15° C.-80° C.
 13. The plasma processing system (10) ofclaim 8, wherein said baffle plate (54) is comprised of low-alloyanodized aluminum and said second cooling passages (80) are machinedtherein.
 14. A gas distribution plate (54) for a plasma processingsystem, comprising: (i) a generally planar central portion (74) havingapertures (76) therein for permitting gas to pass therethrough; (ii)cooling passages (80) for accepting a flow of cooling medium to reducean operating temperature of said baffle plate; and (iii) a coolingmedium inlet (82) and a cooling medium outlet (86) connected to saidsecond cooling passages (80) to permit circulation of a cooling mediumtherethrough.
 15. The gas distribution plate (54) of claim 14, whereinsaid central portion (74) is surrounded by a flange (78), said coolingpassages (80) extending from said flange into said apertured centralportion.
 16. The gas distribution plate (54) of claim 14, wherein saidplate (54) is comprised of low-alloy anodized aluminum and said coolingpassages (80) are machined therein.
 17. The gas distribution plate (54)of claim 14, wherein said cooling medium is a liquid.
 18. The gasdistribution plate (54) of claim 17, wherein said cooling medium iswater.
 19. The gas distribution plate (54) of claim 14, wherein saidcooling medium is a gas.
 20. The gas distribution plate (54) of claim19, wherein said cooling medium is helium or nitrogen.
 21. The gasdistribution plate (54) of claim 14, further comprising a generallyplanar upper baffle plate (155) attached to said baffle plate (54) andseparated by a distance therefrom, said upper baffle plate 155 providedwith apertures
 175. 22. The gas distribution plate (54) of claim 21,wherein said apertures (175) in the upper baffle plate (155) areslightly larger than said apertures (176) in the lower baffle plate(54).
 23. The gas distribution plate (54) of claim 21, wherein saidupper baffle plate (155) is comprised of quartz.